Method and system for fabricating a dental coping, and a coping fabricated thereby

ABSTRACT

A wax model of a required coping is produced using CNC machining techniques based on a virtual model of the coping created from digital data obtained from the intraoral cavity. The dental coping is then fabricated from the wax model.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. Pat Application No.17/247,464, filed Dec. 11, 2020, which is a continuation of U.S. PatApplication No. 16/752,526, filed Jan. 24, 2020, now U.S. Pat No.10,905,530, issued Feb. 2, 2021, which is a continuation of U.S. PatApplication No. 15/811,331, filed Nov. 13, 2017, now U.S. Pat No.10,543,066, issued Jan. 28, 2020, which is a continuation of U.S. PatApplication No. 14/720,426, filed May 22, 2015, now U.S. Pat No.9,844,429, issued Dec. 19, 2017, which is a continuation of U.S. PatApplication No. 13/620,057, filed Sep. 14, 2012, now U.S. Pat No.9,069,914, issued Jun. 30, 2015, which is a continuation of U.S. PatApplication No. 13/189,398, filed Jul. 22, 2011, now U.S. Pat No.8,301,287, issued Oct. 30, 2012, which is a continuation of U.S. PatApplication No. 12/149,102, filed Apr. 25, 2008, now U.S. Pat No.7,996,099, issued Aug. 9, 2011, which is a continuation of U.S. PatApplication No. 11/498,791, filed Aug. 4, 2006, now U.S. Pat No.7,383,094, issued Jun. 3, 2008, which is a continuation of U.S. PatApplication No. 11/214,882, filed Aug. 31, 2005, now U.S. Pat No.7,110,844, issued Sep. 19, 2006, which is a continuation of U.S. PatApplication No. 10/814,653, filed Apr. 1, 2004, now U.S. Pat No.6,957,118, issued Oct. 18, 2005, claiming the benefit under 35 USC §119(e) of U.S. Provisional Pat Application No. 60/459,624, filed Apr. 3,2003, the entire contents of each of which is hereby incorporated hereinby reference in their entirety.

FIELD OF THE INVENTION

This invention relates to teeth restoration, specifically to a methodand system for fabricating dental copings for crowns and/or bridges, andto the copings made thereby.

BACKGROUND OF THE INVENTION

In the field of teeth restoration, metal copings are typically used inthe construction of a dental crown and/or bridge. The metal copingfunctions as the understructure of the crown, and is typically coveredwith a coating of ceramic porcelain composition or a polymer-basedveneering material. The metal coping supports the coating and providesthe required structural strength and rigidity for the restored tooth toresist the forces of mastication.

There are methods in the art for the production of metal coping bycasting it from a wax pattern, for example by the known “lost wax”technique. An accurate working model of the patient’s teeth, whichincludes the preparation (die) of the tooth (or teeth) to be restoredand its surrounding area, is used. As discussed in Kuwata et al., ColorAtlas of Ceramo-Metal Technology (Ishiyaku EuroAmerica, Inc., 1986, pp.96-101), a wax coping, which is an exact replication of the desiredmetal coping, is manually built by wrapping a thin sheet of wax aroundthe working model of the preparation, and is adapted to the preparationsurface. By using a heated carving knife, the margin of the adaptedsheet wax is cut off and the sheet joints are bent and sealed by addingmore wax. The wax margin is further processed in order to correspond tothe margin line of the restoration, i.e. by additional carving and/orwax adding.

The finished wax-up of the coping is then removed from the working modeland invested in a material that solidifies onto the external side of thewax coping and forms a mold (this stage is known as the “investment”stage). The combined structure is then heated such that the wax is burntout, leaving a cavity into which the metal is cast. After hardening, themold is removed from the metal casting.

Another method for producing metal coping involves a direct fabricationof the metal coping based on digital data. U.S. 2002/0137011 disclosesan automated and digital method for the formation of the metal copingfrom a sheet of metallic material, which comprises: scanning a threedimensional image of the die of the tooth or teeth to be restored;digitizing the scanned three dimensional image into digital information,storing the digital information in a computer; feeding the digitalinformation from the computer into a CNC (computerized numericalcontrol) cutting machine; cutting out a section of material of metalliccomposition into a two dimensional configuration representing a twodimensional lay out of the scanned three dimensional image, adapting thecut out section of material over the die so that the material covers thedie surface in close engagement therewith to form a single threedimensional structure having the shape of the die and heat treating thestructure, into a coping, conforming in shape to the die.

WO 03/017864 discloses a method for producing a dental prosthesis suchas a dental coping. The method comprises the following steps: obtainingthree-dimensional digital data relating to a patient’s dentition;designing a virtual prosthesis for the dentition using thethree-dimensional digital data; transmitting digital data correspondingto the virtual prosthesis to an automated prototyping system; producinga prototype of the dental prosthesis with the automated prototypingsystem, the prototype made of a material that can be ablated; coveringat least the prototype with a hardening material and removing theprototype from within said hardening material to produce a mold for thedental prosthesis; casting the dental prosthesis by filling the moldwith a metal and removing the hardening material.

In the case of coping fabrication in the “lost wax” technique, be it themanual production or the automated, prototype production, the wax isused as it is easy to manipulate and allows a high level of accuracy.Typically, soft wax, i.e. wax with relatively high viscosity, is used.Special care must be taken in handling the soft wax, as it is verysensitive to physical stress. Indeed, any damage to the wax-up patternbefore investment (i.e. during its production process or after) maylower the quality of the replicated dental coping.

Of general background interest, the following patents describemanufacturing methods for prostheses. In US 4,663,720 and US 4,742,464an apparatus and method are disclosed for designing a prosthesisstarting with a 3D model of the patient’s dentition obtained by opticalmethods, and directly machining the prosthesis from a blank. In US5,092,022, a prosthesis or a negative mold therefor can be machinedautomatically from suitable materials, with the assistance of a computerwhich takes into consideration, inter alia, the shape of the zone ofimplantation previously obtained. In US 5,452,219, a negative mold for aprosthesis is milled using a machine controlled by a program based on 3Ddata obtained from a tooth model. In US 5,378,154 a method for machininga dental prosthesis is disclosed, wherein the outside visible part ofthe prosthesis is subjected to a material removal operation by means ofa CNC machining tool which follow machining paths that follow 3Dirregularly spaced curved lines. In US 6,126,732, a shaped high-strengthdental ceramic prosthesis is made by pressing a molding compositioncomprising 1-50 wt% glass particles and about 50-99 wt% ceramicparticles to form a ceramic frame, veneering the frame and firing thecoated frame. In US 5,691,905 and US 5,718,585 methods of milling andpolishing a set of negative mold parts are disclosed. In US 6,488,503, aprocess is described for producing an artificial tooth, in whichpolymerizable materials are injection molded into a mold in stages toproduce a solid core applied on an inner layer, which is applied on anexternal layer of the artificial tooth. In US 6,066,274, a deviceincluding an injection molding tool is disclosed for producing asinterable ceramic and/or metallic product using engageable molding toolparts one of which is produced using a wet composition. In US 5,382,164,a method of making restorations is disclosed, comprising: temporarilyrepairing a tooth area to be restored to a final shape, and taking afirst impression of the tooth area to be restored; preparing the toothto be restored, and taking a second impression within the firstimpression to form a physical model of the crown. This model is thenscanned to provide an image thereof, and a computer uses this image tomill the final restoration.

SUMMARY OF THE INVENTION

The present invention provides, in its first aspect, a method and systemfor fabricating a dental coping for dental prosthesis of at least onetooth which is to be fitted over a tooth preparation. The methodcomprises providing three-dimensional (3D) digital data relating to thepatient’s dentition, which includes data representative of the surfacetopology of the preparation and its surroundings. The method furthercomprises generating a three-dimensional (3D) virtual model of a dentalcoping for the tooth, such that the inner surface of the virtual copingfits over a portion of the surface of the tooth preparation in closeengagement. Alternatively, a virtual model of the final requiredrestoration may be created, and the internal surface of the requiredcoping is derived from this model; a suitable external surface for thecoping can be designed in any suitable manner. The method furthercomprises generating a computerized numerical control (CNC) set ofinstructions corresponding to the 3D model of said coping. Based on saidset of instructions, a model coping is fabricated from wax or other lowfusion temperature material, by a computerized numerical control (CNC)milling machine. From the fabricated coping wax model, a dental copingis fabricated. The system comprises means for providingthree-dimensional (3D) digital data relating to the patient’s dentition,which includes data representative of the surface topology of thepreparation and its surroundings. The system further comprises means forgenerating a three-dimensional (3D) virtual model of a dental coping forthe tooth, such that the inner surface of the virtual coping fits over aportion of the surface of the tooth preparation in close engagement. Thesystem further comprises means for generating a computerized numericalcontrol (CNC) set of instructions corresponding to the 3D model of saidcoping. The system also comprises mans for fabricating a model of thecoping from wax or other low fusion temperature material, by acomputerized numerical control (CNC) milling machine, based on said setof instructions. The system further comprises means for fabricating adental coping from the fabricated coping wax model.

The present invention also provides a method and system for thefabrication of a coping wax model that is to be used for fabricating adental coping for a dental prosthesis of at least one tooth that is tobe fitted over a tooth preparation. This method comprises providingthree-dimensional (3D) digital data relating to the patient’s dentition,which includes data representative of the surface topology of the toothpreparation and its surroundings; generating a three-dimensional (3D)virtual model of a dental coping for the tooth, such that the innersurface of the virtual coping fits over a portion of the surface of thetooth preparation in close engagement; generating a computerizednumerical control (CNC) set of instructions corresponding to the 3Dmodel of said coping; and based on said set of instructions, fabricatinga wax coping by a computerized numerical control (CNC) milling machine.The system comprises means for providing three-dimensional (3D) digitaldata relating to the patient’s dentition, which includes datarepresentative of the surface topology of the tooth preparation and itssurroundings; means for generating a three-dimensional (3D) virtualmodel of a dental coping for the tooth, such that the inner surface ofthe virtual coping fits over a portion of the surface of the toothpreparation in close engagement; means for generating a computerizednumerical control (CNC) set of instructions corresponding to the 3Dmodel of said coping; and based on said set of instructions, means forfabricating a wax coping by a computerized numerical control (CNC)milling machine.

The term “tooth preparation” as used herein refers both to one or moretooth stumps or pivots (also known as cores or posts) prepared by thecare provider on the basis of an original tooth or an implant whichserves as a basis for the dental prosthesis (e.g. crown or bridge).

The term “dental coping” as used herein refers to a support structurefor a crown, i.e. structure that cups only one tooth, as well as asupport structure for a bridge, i.e. structure that cups more than onetooth. The term “dental coping” as used herein, also refers to the cup,which may be made from metals or ceramics, for example, and all otherprosthesis elements such as connectors and pontics, as the case may be.The dental coping may be fabricated from suitable materials such asmetal, ceramo-metal materials, etc.

The 3D digital data may be obtained by a number of ways known per se.For example, such digital data may be obtained in a manner as describedin WO 00/08415, U.S. Pat Application No. 2002/0137011 or in any of U.S.Pat 6,099,314 and 6,334,853, or any combination thereof. The 3D dataincludes the surface topology of the preparation, as well as itssurroundings. Furthermore, such 3D digital data may also comprise otherdata, for example, data that was added by the orthodontist or a dentaltechnician, such as the preparation’s finish line.

The 3D virtual model of the dental coping may be produced in a number ofways. By one example, the dentist, orthodontist, etc. (to be referred toherein collectively as the “care provider”) designs the overall outersurface of the tooth prosthesis and then, based on known considerationsof enamel thickness as well as coping thickness, the coping is designedso as to fit below the surface of the tooth prosthesis and over thetooth preparation. As known per se, some room needs to be reserved foradhesive materials.

By another example, the coping is designed primarily on the basis of thesurface topology of the preparation and other factors such as the copingwall’s thickness, finish line data, etc.

The generation of the virtual 3D coping data may be automatic, manual ora combination thereof.

The term “wax” includes any material that is relatively hard and lendsitself to machining, particularly milling, while having a sufficient lowmelting point and appropriate kinematic viscosity that renders itsuitable for use in a lost wax process or the like.

The wax that should be used in accordance with the invention is hard anddurable that lends itself to milling in a milling machine. Anotherrequirement of the wax is that after melting, it should have a viscositysufficiently low to be usable in a lost wax technique known per se inthe art of metal casting.

A typical wax that can be used in accordance with the invention is suchhaving a melting point and congealing point of 55-80° C. and a kinematicviscosity of less than 90 m²sec. at about 100° C. .

As will be appreciated, the coping prepared in accordance with theinvention may be suitable for a single tooth, (in the case of a singletooth prosthesis), or a coping that serves as a basis for a bridge.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carriedout in practice, a preferred embodiment will now be described, by way ofnon-limiting example only, with reference to the accompanying drawings,in which:

FIGS. 1A-1E illustrate an exemplary scenario for the fabrication of adental coping in which the invention is implemented;

FIG. 2 shows a block diagram of fabrication processes according to theinvention.

FIG. 3 shows a block diagram of fabrication system according to theinvention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

FIGS. 1A-1E illustrate an exemplary scenario for the fabrication of adental coping in which the invention is implemented. The scenario iscarried out with the aid of a computer system, the operation of whichwill be explained later on. FIG. 1A shows a section 10 of a patient’steeth (part of the patient’s upper jaw, in this example), in which toothprosthesis is to be fitted over tooth preparation 12. In the example ofFIG. 1A, the root and base of the tooth 12 are sufficiently strong andhealthy, and the care provider prepared the tooth for the crown byremoving a portion of the enamel and dentin. If the tooth to be restoredis severely decayed or weak, then it may be necessary to insert a metalimplant or pivot (also known as cores or posts) by any one of a numberof ways known per se.

An exemplary system 300 for carrying out the process of the invention isillustrated in FIG. 3 .

The 3D digitized data of the intraoral cavity, including the dentitionand associated anatomical structures of a patient is obtained, and thussuitable equipment for scanning a patient’s teeth is used by the careprovider to acquire the 3D data. The production of the virtual 3Dworking model of the preparation and its surroundings is known per-se.

As shown in FIG. 1B, for example, the care provider captures an image ofthe preparation and its surroundings with a probing device 20.Advantageously, a probe for determining three dimensional structure byconfocal focusing of an array of light beams may be used, for example asmanufactured under the name of PROSTHOCAD or as disclosed in WO00/08415, the contents of which are incorporated herein in theirentirety. Alternatively, scanning of the dental cavity to provide the 3Ddata may be accomplished using a suitable apparatus, for example asdisclosed in any one of US 4, 837,732, US 4,611,288, US 6,594,539, US6,402,707, US 6,364,660, US 2002/0028418, US 2002/0058229, US 5,652,709,US 4,575,805, US 5,733,126, US 5,880,962, US 4,742,464, US 4,663,720, WO02/071306 mutatis mutandis. The contents of these publications areincorporated herein in their entirety by reference thereto.

The 3D data obtained by the probe may then be stored in a suitablestorage medium, for example a memory in a computer workstation, forfurther processing, as described herein.

Alternatively, a negative cast or impression is taken of the patient’steeth, in a manner known in the art, and this negative model and apositive cast is made from this model suitable for scanning. Thepositive cast may be scanned by any method known in the art, includingusing the aforesaid probe manufactured under the name of PROSTHOCAD oras disclosed in WO 00/08415. Alternatively, the negative model itselfmay be scanned.

Alternatively, a composite positive-negative model may be manufacturedfrom the original negative model. Thereafter, the positive-negativemodel may be processed to obtain 3D digitized data, for example asdisclosed in US 6,099,314, assigned to the present assignee, and thecontents of which are incorporated herein in their entirety.

Alternatively, the 3D digitized data may be obtained in any othersuitable manner, including other suitable intra oral scanningtechniques, based on optical methods, direct contact methods or anyother means, applied directly to the patient’s dentition. Alternatively,X-ray based, CT based, MRI based, or any other type of scanning of thepatient or of a positive and/or negative model of the intra-oral cavitymay be used. The digitized data may be associated with a completedentition, or of a partial dentition, for example such as a preparationonly of the intra oral cavity.

Referring to FIG. 3 , a virtual 3D working model 22 is digitallyproduced by a processor, 29 and may well be displayed on display 24.

FIG. 1C shows the virtual working model 22 in a magnified manner, withits finish line 26 (also known as the margin line) that was eithergenerated automatically or marked by the care provider. The virtualmodel 22 and the finish line 26 data, and perhaps additional 3D datathat relates to the patient’s dentition, are processed and then input toa CAD (Computer-Aided Design) unit (not shown) that allows for thedigital design of the dental coping, resulting in the virtual coping 30,shown in FIG. 1D.

The virtual coping 30 may then be further processed by a CAM(Computer-Aided Manufacture) unit (not shown) to generate a digital setof instructions T that are fed into a CNC (computerized numericalcontrol) milling machine 260, from which a wax coping 40 (as the oneshown in FIG. 1E) is milled using wax or the like supplied from supply270. Wax coping 40 is made of relatively hard, durable wax or similarmaterial. In particular, the coping 40 is made from a material that onthe one hand lends itself to milling in a milling machine, while on theother hand has a low melting point and after melting, it has a kinematicviscosity sufficiently low to be usable in a lost wax technique knownper se in the art of metal casting. Preferably, such a material has amelting point and congealing point of about 55° C. to about 80° C. and akinematic viscosity of less than 90 m²sec. at about 100° C. .

The desired dental coping 90 is then produced from the wax coping,according to common dental practice, via suitable manufacturing means280.

The finish line data can be generated for example, in a manner disclosedin USSN 10/623,707 and WO 04/008981 also assigned to the presentassignee, and the contents of which are incorporated herein in theirentirety.. Alternatively, the finish line may be generated using methodsdisclosed in US 5,266,030 the contents of which are incorporated herein.The virtual generation of the finish line may be incorporated as anintegral component in the method of the invention.

The additional 3D data that relates to the patient’s dentition includes,inter-alia, information relating to the surrounding of the tooth to berestored, e.g. 3D representation of the patient’s dentition, includingthe upper and lower jaws and their occlusion relationship. Suchinformation is needed, e.g. for the design of the dental crown, and canbe generated for example, as disclosed in US 6,099,314 and US 6,334,853.

The virtual model of the desired coping can be generated in severalways. According to one possible way, the care provider designs theoverall outer surface of the tooth prosthesis, based on knownconsiderations such as enamel thickness, as well as coping thickness andothers. The coping is designed so as to fit below the surface of thetooth prosthesis and over the tooth preparation. By another example, thecoping is designed primarily on the basis of the surface topology of thepreparation and other factors such as the coping wall’s thickness,finish line data, etc.

In particular, the external surface of the coping, which eventuallymates with a cap or the like which may be single-layered ormulti-layered, is designed according to predetermined criteria, as knownin the art, to provide the required mechanical properties required fromthe restoration.

The virtual coping 30 may also be created in other ways. For example, aphysical model of the restoration may be created in any suitable manner,for example as disclosed in US 5,382,164, the contents of which areincorporated herein in their entirety. The inner surface of such amodel, preferably including the finish line, may be scanned in anysuitable manner, similar, for example to that described above for thepreparation, mutatis mutandis, Alternatively, a virtual model of thefull restoration may be used to provide the internal surface andpreferably the finish line for the coping. Then, an external surface forthe coping may be designed according to any suitable criteria, forexample as described above, and the virtual model corresponding to theexternal surface may be joined to the virtual model of the inner surfaceto provide the virtual coping 30.

The method of the present invention in fact makes use of the “lost wax”technique, by utilizing relatively hard, durable wax, which can bemilled to the desired pattern by a CNC milling machine.

FIG. 2 shows a block diagram of fabrication processes 100 according tothe invention. At step 110, a three-dimensional (3D) digital data isprovided. The 3D digital data relates to the patient’s dentition,including data representative of the surface topology of the preparationand its surroundings. At step 120, a 3D virtual model of a dental copingis generated.

At step 130, a CNC (Computerized Numerical Control) set of instructionscorresponding to the 3D virtual model of the desired coping isgenerated, and fed into a CNC milling machine for the fabrication of awax coping (step 140), wherein a wax coping is produced from a suitableblock of wax or the like.

Optionally, and particularly when the final prosthesis is a bridge, waxreplicas of suitable connectors and/or one or more pontics are made,either manually or by any suitable method, including machining, castingand so on, indicated at 240 in FIG. 3 . Then, the connectors and/orpontics are joined to the wax copings of the abutment teeth in asuitable manner, for example as is known in the art per se. The metal orceramic structure for the bridge is then made from the wax model thereofin a similar manner to that described below for a single coping, mutatismutandis.

At step 150, the dental coping is fabricated from the wax coping. Thismay be accomplished in any number of ways, known per se in the art. Forexample, the wax coping is invested in a material that solidifies ontothe external side of the wax coping and forms a mold. After theinvestment stage, the combined structure is then heated such that thewax is burnt out, leaving a cavity. Into this cavity, a suitable moltenmetal may be injected, and after hardening, the mold is removed from themetal casting to provide a metal coping. Such a lost wax process may besimilar to the process used for the production of restorations asdescribed by Ivoclar Vivadent Ltd. regarding the IPS Empress system inhttp://www.ivoclar.co.uk/technician/nonmetal2.html, mutatis mutandis,for example Alternatively, a suitable ceramic molding composition may bepressed into the cavity, for example as described in US 6,126,732,mutatis mutandis, the contents of which are incorporated herein in theirentirety. Alternatively, sintering methods may be applied to the mold toproduce a ceramic coping.

Alternatively, the wax coping may be scanned and the coping produced ina manner similar to the production of crowns and bridges, as describedby DeguDent regarding the Cercon system inhttp://www.degudent.com/Products/Cercon_smart_ceramics/index.asp,mutatis mutandis.

The dental coping manufactured according to the present invention isthus derived from a wax model, which due to its relatively softness canbe machined to a smoother surface texture than is possible whenmachining the coping directly from the desired final material such asmetal or a ceramic. Accordingly, dental copings produced using themethod of the invention using the wax for preparing a mold arecorrespondingly smoother, and furthermore it is possible to include finedetails in the final coping, with respect to copings produced usingdirect material removal methods applied to the final material.

Furthermore, the wax-based method of the present invention for producingthe dental coping has some advantages over direct material removalmethods that are used elsewhere for producing the coping directly fromthe desired final material. For example less wear and breakage areexperienced by the machining tool, and thus lowers costs. Furthermore,deformations of the tool, when a direct contact tool such as for examplea mechanical tool is used, is less likely, and thus less deviations fromthe nominal dimensions of the coping with respect to the virtual modelthereof occur than when producing a coping directly from a metal orother hard material.

The invention allows to gather the 3D data that represents the patient’sdentition in one place (say, the care provider’s clinic), to design thevirtual coping model at the clinic or at a remote location, to generatethe CNC set of instructions at another place and to fabricate the waxcoping at a yet another location. Furthermore, the invention allows forthe fabrication of the wax coping and the dental coping at differentlocations without damaging the quality of the dental coping due todeformations in the coping wax model. It should be noted thatadditional, intermediate steps in which digital data is transmittedbetween remote locations might be carried-out as part of method 100, forexample between steps 110 and 120, etc.

The invention is not bound by the specified example of FIGS. 1A-1E and,accordingly, other scenarios may be used in addition or in lieu of theabove, depending upon the particular application. Specifically, theinvention can also be utilized in a less “digitized” scenario, forexample one in which the care provider gathers the relevant informationrelating to the patient’s dentition in a non-digitized manner (e.g. bytaking a physical impression of the patient’s dentition), and thepatient’s dentition data is digitized later on, at a laboratory.

Furthermore, the invention can be utilized for the fabrication of thedental prostheses as a whole, as needed, for example, when restoring thetooth with a gold prosthesis. In that case, a wax model of the desiredprosthesis is fabricated, from which a whole metal prosthesis isreplicated.

What is claimed is:
 1. A method for the fabrication of a dentalprosthesis of at least one tooth to be fitted over a tooth preparation,comprising: receiving input adjusting a marking of a finish linepreviously digitally marked on a three-dimensional virtual model of apatient’s dentition, the marking being between a prepared portion of atleast one tooth and an unprepared portion of the at least one tooth;generating a virtual model of a dental prosthesis based on the virtualmodel of the patient’s dentition and the adjusted finish line, thevirtual model of the dental prosthesis having an tooth facing surfacebased on the portion of the virtual model representative of the preparedportion of at least one tooth and an external surface based the preparedportion of at least one tooth and an enamel thickness of a toothpreparation; and outputting the virtual model of the dental prosthesisto a fabrication machine for fabricating a physical model based on thevirtual model.
 2. The method of claim 1, further comprising generatinginstructions that instruct the fabrication machine to fabricate thephysical model.
 3. The method of claim 2, wherein the physical model isa wax model.
 4. The method of claim 3, further comprising fabricating adental prosthesis from the wax model.
 5. The method of claim 1, whereinthe fabrication machine is a CNC milling machine.
 6. The method of claim1, wherein the virtual model is generated based on scan data receivedfrom an optical scanner.
 7. The method of claim 6, wherein the scannercomprises a probe for determining a three-dimensional structure byconfocal focusing of an array of light beams.
 8. The method of claim 6,wherein the scanning is performed directly on an intraoral cavitycomprising the prepared tooth.
 9. The method of claim 1, wherein thefabricating is carried out according to a lost wax process.
 10. Themethod of claim 1, wherein the dental prosthesis is a crown prosthesis.11. The method of claim 1, wherein the dental prosthesis is a bridgeprosthesis.
 12. The method of claim 11, further comprising providing waxreplicas of suitable connectors and/or one or more pontics.
 13. Themethod of claim 1, wherein the virtual model of the prosthesis furthercomprises an external surface that is an occlusal facing surface of theprosthesis.
 14. The method of claim 1, further comprising: providing thethree-dimensional virtual model of the patient’s dentition, and whereinmarking the finish line on the three-dimensional virtual model of thepatient’s dentition includes marking the finish line on the provided thethree-dimensional virtual model of the patient’s dentition.
 15. A methodfor the fabrication of a dental prosthesis model shaped to be fittedover a prepared tooth, comprising: receiving user input adjusting amarking of a finish line previously digitally marked onthree-dimensional data representing a surface topology of a preparedtooth between a prepared portion of the prepared tooth and an unpreparedportion of the prepared tooth; generating a virtual model of a dentalprosthesis based on the three-dimensional data, the virtual model havinga tooth facing surface based on the prepared portion of at least onetooth and an external surface based on the prepared portion of at leastone tooth and an enamel thickness of a tooth preparation; and outputtingfabrication data based on the virtual model of the dental prosthesis forfabricating a physical model based on the virtual model.
 16. The methodof claim 15, wherein the fabrication data includes instructions thatinstruct a fabrication machine to fabricate the physical model.
 17. Themethod of claim 15, wherein the physical model is a wax model.
 18. Themethod of claim 17, further comprising fabricating a dental prosthesisfrom the wax model.
 19. The method of claim 15, wherein the fabricationmachine is a CNC milling machine.
 20. The method of claim 15, whereinthree-dimensional data representing a surface topology of a preparedtooth if generated based on scan data received by scanning using anoptical scanner.